Currently, palletizing bundles is typically done either manually or by automated robotic systems using bundle gripper heads or end effectors attached to manipulator arms. Manual palletizing is undesirable in several respects. At a minimum, one person is required for each stacker and/or pick-up location, and where multiple stackers or pick-up locations are present overhead costs can become a significant detriment to system profitability. With speeds of printing presses continuing to increase, e.g. up to 110,000 signatures/hour, manual palletizing can present a formidable obstacle to the maintenance of high throughput post press while keeping the number of laborers to a minimum. In some instances, reduced throughput is simply not acceptable when the printed material is time sensitive such as with most advertising material.
The laborers in these jobs tend to be lower skilled and thus are more likely to damage products when grabbing a bundle from its pick-up location, carrying it to the pallet, and properly locating the bundle on the pallet. Low skilled laborers are also generally lower wage earners so that there typically is greater turnover rates in these jobs increasing expenses associated with low retention rates such as hiring and training costs and the like. Further, where there is manual labor involved, injuries that limit the worker' ability to perform their job can create lost productivity further eroding profits.
Power assisted devices or bundle gripping heads to enable workers to lift and transport bundles for being palletized have been attempted. However, they generally have not realized their full potential because of the difficulty workers have in maneuvering the devices, particularly when raising or lowering these devices while carrying bundles.
Automated gripping heads used with robot arms are generally faster and do not present many of the problems set forth above that more manual systems can create. These automated heads tend to be very expensive from both a cost of purchase and cost to maintain standpoint. One significant drawback in their use is that the gripping or grasper heads tend to be limited in terms of the variations in product format or size they can handle. Specifically, the supports or fork members they use to pick-up the bundles are usually fixed in their length and/or in their relative lateral position with respect to each other. This creates problems with customers who are dealing with wide variations in product format, particularly in the low-end market including such things as “junk” mail and cards for CD cases and the high-end gravure market including tabloids as well as other uncommon signature formats.
For these customers, the fixed fork grasper units have to have their fork members sized to the smallest width and length format product to be handled so that the form members do not project out from underneath the bundles being lifted, transported and palletized. Projecting forks can create a safety hazard and make it extremely difficult to place the bundles on the pallet without damaging or marking bundles already present on the pallet.
The product format will in large part determine the pattern of the bundles as placed on a given sized pallet to ensure a stable stacking of the bundles on the pallet. For instance, due to the presence of spines that can create an uneven build-up of signatures in a bundle, there can be a sloped upper surface on the bundles. Stacks of such bundles one on top of the other with signature spines aligned will cause a cumulative build-up of sloped signatures with the slope becoming more pronounced with each bundle. To address this problem, the bundles are patterned to be blocked in against each other in a layer of bundles on the pallet so that adjacent bundles will tend to resist any shifting of signatures disposed toward the top of the sloped bundles. Furthermore, the bundles particularly at a corner in a layer of bundles may not be oriented with their length or width running in the same direction as the adjacent bundles due to the product format relative to the pallet size. It is also true that adjacent layers of bundles on the pallets may be arranged differently for stability purposes.
In sum, it is important that the automated gripper units be flexible and agile enough to accommodate the differing product and pallet sizes and the various patterns in which the bundles are to be deposited on the pallets. Of course, having fork members that project beyond the bundle significantly impairs the maneuvability necessary to be able to place bundles down in tight fitting patterns on pallets such as where they are to be in blocking relation with other bundles without engaging and damaging these bundles on the pallet.
On the other hand, having the fork members sized to the smallest product format to avoid the projecting fork problem described above creates significant disadvantages when larger sizes of products are to be palletized. In this instance, the signatures, if wider than the laterally spaced forks will hang over the sides of the forks, and if longer than the length of the forks will hang over the ends creating a drooping condition of the bundle during transport and deposit onto the pallet. Drooping bundles make it more likely that portions hanging over the sides or ends of the bundle supports will catch when being deposited folding over and damaging these hanging bundle portions. Furthermore, with these oversized bundles relative to the fixed forks and where the drop-off level for the bundle is higher than the pick-up level, there is a need for raising the bundles higher than otherwise would be necessary to clear the surface on which the bundle is to be deposited, be it the top of a lower bundle or the pallet itself. With automated robotic systems, the extra raising of the bundle gripper needs to be programmed into the software controlling the movements of the robot arm. As is apparent, the extra time required of the robot arm to execute its movement to raise the drooping bundles to a clearance level so they do not engage other bundles on the pallet undesirably increases cycle time.
There have been bundle gripping units that have generally proposed incorporating format adjustment capabilities although these capabilities generally have not been optimized from an ease of use or implementation standpoint, see U.S. Pat. No. 6,129,504, commonly assigned to the assignee herein. However, this and other such units still suffer from the shortcoming that they only pick-up, transport and deposit one bundle at a time. While these units are generally fast enough to handle bundles from a single signature stacker to be deposited on a single pallet, they can compromise cycles times in other layouts such as where there are multiple stackers and/or pallets from which bundles are to be picked-up and on which they are to be deposited, respectively.
The sloping upper surface of bundles also can lead to problems with many grippers that employ rigid bars or clamp members to engage and push signatures down for clamping the bundles against the supports or forks thereunder. Because of the slope of the bundles, and the rigidity of the clamping members or bars, when the bars are brought down into engagement with the top of the bundle, they will first engage the higher portion of the top of the bundle and start to push it down before engaging against the lower portions fo the bundle top. Since the rigid clamp members are pushing down on only the raised top portion of the bundle prior to engagement with the more lower portions, the signatures in the bundle will tend to want to slide or “squirt” out of the bundle stack by shifting in the direction of the non-engaged bundle portions or downslope. This is especially true where the signatures include coatings with slip agents such as silicon and wax materials incorporated to minimize ink rub-off problems in the bundle. Thus, the prior bundle grasper disclosed in the '504 patent needed to constrain the bundle from lateral shifting upon clamping via the use of surrounding guides along all four sides of the bundle.
Accordingly, there is a need for an operator controlled bundle transport system and method using a bundle carrier that allows the operator to easily maneuver the bundle in a manner that is highly responsive to operator control. A further need exists for a gripping apparatus and method that provides improved flexibility in handling of different product formats. Further, it is desirable for such an apparatus to allow for stable palletizing of the bundles while at the same time achieving improved cycle times relative to those achieved with prior bundle gripper units. A bundle gripping apparatus that is easy to use would also be desirable.